1、一个线程epoll_wait时，另一个线程调用epoll_ctl是安全的。

2、使用edge触发，在socket有数据到来后，不收取数据，再次调用epoll_ctl将socket加入，仍会触发下一次动作。

asio用该方法来发送通知。

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

using namespace std;

void reset_ev(int epfd, int fd)

{

while (1)

{

std::chrono::milliseconds dura(2000);

std::this_thread::sleep_for(dura);

struct epoll_event ev;

ev.data.fd = fd;

ev.events = EPOLLIN | EPOLLET;

epoll_ctl(epfd, EPOLL_CTL_MOD, fd, &ev);

}

}

int main(int argc, char *argv[])

{

int fd[2];

if (socketpair(PF_LOCAL, SOCK_STREAM, 0, fd) < 0)

{

perror("socketpair");

return 0;

}

write(fd[1], "c", 1);

int epfd = epoll_create(1024);

struct epoll_event ev;

ev.data.fd = fd[0];

ev.events = EPOLLIN | EPOLLET;

epoll_ctl(epfd, EPOLL_CTL_ADD, fd[0], &ev);

std::thread t(&reset_ev, epfd, fd[0]);

epoll_event events[20];

for (;;)

{

int nfds = epoll_wait(epfd, events, 20, -1);

cout << "epoll_wait returns " << nfds << endl;

for (int i = 0; i < nfds; ++i)

{

cout << "fd:" << events[i].data.fd << " triggered." << endl;

}

}

}